ape030_bennion_2012_o.pdf

NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.

Electric Motor Thermal Management

Kevin Bennion National Renewable Energy Laboratory May 16, 2012

Project ID #: APE030

This presentation does not contain any proprietary, confidential, or otherwise restricted information.

2

Overview

Project Start Date: FY 2010 Project End Date: FY 2013 Percent Complete: 60%

• Cost • Weight • Performance & Life

Total Project Funding: DOE Share:$1,275K (FY10-FY12)

Funding Received in FY11: $450K Funding for FY12: $425K

Timeline

Budget

Barriers and Targets

• Interactions / Collaborations – University of Wisconsin (UW) – Madison

(Thomas M. Jahns) – Oak Ridge National Laboratory (ORNL) – Motor Industry Representatives

• Project Lead – National Renewable Energy Laboratory

Partners

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Relevance/Objectives

The transition to more electrically dominant propulsion systems leads to higher-power duty cycles for electric drive systems.

Continuous Operating Limit

Torq

ue

Speed

Thermally Limited Area of Operation

Transient Operating Limit

Thermal management is needed to reduce size and improve performance of electric motors. • Meet/improve power capability within

cost/efficiency constraints • Reduce rare earth material costs (dysprosium)

Targets Efficiency (%)

Cost ($/kW)

Weight (kW/kg)

Volume (kW/L)

4

Relevance/Objectives

The transition to more electrically dominant propulsion systems leads to higher-power duty cycles for electric drive systems.

Continuous Operating Limit

Torq

ue

Speed

Thermally Limited Area of Operation

Transient Operating Limit

Objectives • Quantify opportunities for improving cooling technologies for electric motors • Link thermal improvements to their impact on Advanced Power Electronics and

Electric Motors (APEEM) targets • Increase publicly available information related to motor thermal management

Addresses Targets • Translates cooling performance improvements into impacts on program targets • Prioritizes motor thermal management efforts based on areas of most impact

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Milestones Date Milestone or Go / No-Go Decision Point Oct. 2011

Milestone report • Analytical and 3D finite element analysis (FEA) models for determining effective

conductivity of composite materials as applied specifically to motor slot windings • Results of initial thermal property testing of motor lamination materials • Method of evaluating loss distributions within the electric motor for different operating

conditions (in collaboration with University of Wisconsin – Madison) • Development of stator thermal model validated against published data • Parameter sensitivity study of thermal design factors for motor stator cooling

Jan. 2012

Go/No-Go • Completed selected motor lamination material thermal property tests • Decided to not expand material tests at this time Milestone (intermediate) • Completed thermal sensitivity analysis for interior permanent magnet (IPM) motor

stator and rotor utilizing test data provided by ORNL

Jul. 2012 Go/No-Go • Thermal sensitivity analysis shows significant impact common to multiple motor

configurations leading to future project proposals for specific cooling enhancements

Sept. 2012 Milestone report • Lamination material thermal properties, motor thermal sensitivity analysis, and oil heat

transfer experimental data

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Approach/Strategy

Package Mechanical

Design

Cooling Technology Selection

Thermal Design Targets

• Characterize fundamental oil-cooling heat transfer performance • Initiate experiments to identify cooling limitations

(durability)

• Complete thermal FEA and lumped parameter thermal models for cooling parameter sensitivity analysis (UW, NREL) • Complete material thermal property tests (NREL)

Credit: Kevin Bennion, NREL Lamination Stack

Courtesy of T. M. Jahns / S. McElhinney, UW - Madison

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Approach/Strategy Approach/Strategy

Motor thermal analysis is a challenge

•Complicated •Many unknowns

Absolute results of analysis could change, but the goal is to identify trends for improvements in motors

Try to make intelligent choices to ensure quality: •Results not focused on single motor

design •Assumptions and results compared

to published literature •Model results compared against

test data •Collaborations with motor

designers •Component testing

Challenges

Variation in Motor Configuration

Identify challenges across motor configurations

Stator – Distributed Winding

IPM – Distributed Winding

IPM - Concentrated winding

Heat Generation Distribution and

Variation

Evaluate Multiple Operating Conditions

(low speed/high torque, high speed/ low torque)

Test data comparison

Collaborations

University of Wisconsin

Oak Ridge National Laboratory

Material Properties and Interfaces

Literature searches and in-house thermal characterization

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Technical Accomplishments and Progress

Measured bulk thermal conductivity of lamination materials • Tests performed with Xenon Flash

equipment • Four samples of each material tested • General data for silicon steels lists the

thermal conductivity to be between 20-30 W/m-K [1].

Data range from four samples of each material

[1] J. R. Hendershot and T. J. E. Miller, “Design of brushless permanent-magnet motors.” Magna Physics Pub., 1994.

Lamination Material Tests

All Images - Credit: Kevin Bennion, NREL

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Measured specific heat of lamination materials • Tests performed with differential

scanning calorimeter • Two samples of each material tested • Provides data for specific heat over a

range of temperatures • Generally available data for silicon

steels list the specific heat to be 0.49 J/(g-K) [1].

Data range from two samples of each material (two of each thickness)

0.4

0.45

0.5

0.55

0.6

-40 10 60 110 160Cp

(J/g

-K)

Temperature (°C)

Specific Heat M19

[1] J. R. Hendershot and T. J. E. Miller, “Design of brushless permanent-magnet motors.” Magna Physics Pub., 1994. All Images - Credit: Kevin Bennion, NREL

Lamination Material Tests

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Data range from two samples of each material

0.4

0.45

0.5

0.55

0.6

-40 10 60 110 160

Cp (J

/g-K

)

Temperature (°C)

Specific Heat ARNON

0.4

0.45

0.5

0.55

0.6

-40 10 60 110 160

Cp (J

/g-K

)

Temperature (°C)

Specific Heat HF10

Data range from two samples of each material

Additional specific heat measurements for sample materials

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Meter Block

Lamination

Lamination

Lamination

Meter Block

Credit: Kevin Bennion, NREL

Lamination Stack

Quantified thermal contact resistance between laminations • Tests performed with ASTM interface test stand • Tested at multiple pressures and lamination layer

counts • Data used to approximate effective cross

lamination thermal conductivity • Data support modeling activities • Expands publicly available data

Add Picture

Meter Block

Meter Block

Credit: Sreekant Narumanchi, NREL

Measure total thermal resistance of lamination stack

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•Contact resistance decreases with pressure

Meter Block

Lamination

Lamination

Lamination

Meter Block

Calculated contact resistance from measured bulk material properties and lamination stack resistance measurements

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•Effective thermal conductivity increases with pressure •Effective thermal conductivity levels

off after the number of laminations increases beyond 50

Meter Block

Lamination

Lamination

Lamination

Meter Block

Calculated effective conductivity from measured bulk material properties and lamination-to-lamination contact resistance

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H. Kanzaki, K. Sato, and M. Kumagai, “A Study of an Estimation Method for Predicting the Equivalent Thermal Conductivity of an Electric Coil,” Trans. JSME, 56 (526), 1990, 1753-1758.

Quantified thermal properties for slot windings • Expanded on published analytical methods to include wire, filler material, and

insulation material (3-component analytical model) • Developed parametric FEA modeling capabilities to characterize multi-dimensional

heat spreading effect across slot windings • Supports motor thermal modeling activities

Heat flow is multidimensional

FEA Polarized

FEA

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Completed thermal sensitivity analysis of surface permanent magnet motor stator • Developed 3D thermal model • Validated model against published data • Confirmed thermal property (material/contact) and

boundary condition assumptions

J. Lindström, “Thermal Model of a Permanent-Magnet Motor for a Hybrid Electric Vehicle,” Department of Electric Power Engineering, Chalmers University of Technology, Göteborg, Sweden, 1999.

End Winding

Stator Laminations

Case

Slot Winding

Case Cooling

Validation of model assumptions

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Technical Accomplishments and Progress Cooling sensitivity analysis with different winding/core heat distributions at fixed heat exchanger performance

End Winding

Stator

Case

Note: Axial direction is along the length of the motor

•Highlights critical thermal paths •Cooling location and heat

distribution impact results

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End Winding

Stator

Case

Technical Accomplishments and Progress Change in available power output versus relative change in effective thermal conductivity for case-cooled configuration

Significant potential for improvement before effects diminish

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Technical Accomplishments and Progress (a) (b)

(c) (d)

Convection coefficients, shown in yellow, applied to the (a) case, (b) rotor face, and (c) & (d) end windings.

Operating Point Loss Distribution

Dataset Power Speed Torque Core Loss Winding Loss

[W] [RPM] [Nm] [W] [W]

1 25,000 5,000 47.75 87% 13%

2 33,500 3,000 106.6 70% 30%

3 33,500 3,000 106.6 70% 30%

4 33,000 5,000 63.03 83% 17%

5 33,000 5,000 63.03 83% 17%

6 33,500 7,000 45.70 85% 15%

7 50,000 5,000 95.49 76% 24%

8 50,000 5,000 95.49 76% 24%

Completed thermal sensitivity analysis for interior permanent magnet motor application (stator and rotor) • Developed 3D thermal model of

permanent magnet motor stator and rotor

• Validated model against test data provided by ORNL

• Dataset with longest run time selected for estimation of boundary conditions

• Remaining data sets used for model validation

•Builds on previous stator model parameter assumptions and validation • Expands analysis to include rotor

19


End Winding Temperature Case Temperature

•Model performance is comparable to test data •Shorter duration tests show less agreement in

case temperature because steady-state temperatures have not been reached

Model comparison to experimental data

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Improved cooling methods can increase power by increasing heat exchanger cooling performance

Current Operating Point (Baseline Performance)

IPM Motor with Stator and Rotor

Peak heat rejection versus cooling performance

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Technical Accomplishments and Progress Sensitivity in power output capability for 20% increase in material thermal conductivity

• For high-speed, low-torque situations, the motor sees a primary benefit from improvements in the thermal conductivity of the rotor • Convection cooling performance impacts

results

Note: “Nominal h” refers to the baseline cooling performance, “High h” represents an aggressive cooling condition

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• For low-speed, high-torque situations, the motor benefits from thermal conductivity improvements in the slot winding, stator core, and case contact • Convection cooling performance impacts results

Note: “Nominal h” refers to the baseline cooling performance, “High h” represents an aggressive cooling condition

Sensitivity in power output capability for 20% increase in material thermal conductivity

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Collaboration and Coordination

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• University – UW – Madison (Thomas M. Jahns)

o Support with electric motor expertise

• Industry – Motor industry suppliers, end users, and researchers

o Input on research and test plans

• Other Government Laboratories – ORNL

o Support from benchmarking activities o Ensure thermal design space is appropriate and modeling assumptions are

consistent with other aspects of APEEM research – Other VTP areas

o Collaborate with VTP cross-cut effort for combined cooling loops

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Proposed Future Work

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Package Mechanical

Design

Cooling Technology Selection

Thermal Design Targets

Cooling Technology Selection • Characterize oil-cooling heat transfer

coefficients • Initiate cooling durability tests

(winding insulation) • Go/No-Go for FY13

– If improvement in cooling performance shows impact on total thermal performance, pursue efforts to characterize improved oil-cooling approaches

– Continue cooling durability tests

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Proposed Future Work

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Package Mechanical

Design

Package Mechanical Design • Complete thermal sensitivity analysis

and model validation for concentrated winding motor with University of Wisconsin (FEA and lumped parameter thermal analysis)

• Quick look at methods to enhance internal heat spreading

• Go/No-Go for FY13 – If motor cooling sensitivity

analysis shows common areas for thermal improvement, initiate R&D on critical factors



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Summary

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Relevance • Impacts the transition to more electrically dominant propulsion systems

with higher continuous power requirements • Enables improved performance of non-rare earth motors • Supports lower cost through reduction of rare earth materials used to meet

temperature requirements (dysprosium) • Applies experimental and analytical capabilities to quantify and optimize

the selection and design of effective motor cooling approaches Approach/Strategy Developed process to meet challenges of motor thermal management • Identify thermal improvements across a range of motor configurations • Evaluate multiple operating conditions (loss distributions) • Engage in collaborations with motor design experts • Perform in-house characterization of material and interface thermal

properties

27

Summary

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Technical Accomplishments • Measured bulk thermal conductivity of lamination materials • Measured specific heat of lamination materials • Quantified thermal contact resistance between laminations • Quantified thermal properties for slot windings • Completed thermal sensitivity analysis for surface permanent magnet

motor stator • Completed thermal sensitivity analysis for interior permanent magnet

motor application (stator and rotor)

Collaborations • Collaborations established with research and development partners

– University of Wisconsin – Madison – Oak Ridge National Laboratory – Motor industry representatives: Manufacturers, researchers, and end

users (light duty and heavy duty)

For more information, contact:

Principal Investigator Kevin Bennion [email protected] Phone: (303)-275-4447 APEEM Task Leader:

Sreekant Narumanchi [email protected] Phone: (303)-275-4062

Acknowledgments:

Susan Rogers and Steven Boyd, U.S. Department of Energy Tim Burress, Oak Ridge National Laboratory Team Members:

Justin Cousineau Douglas DeVoto Mark Mihalic Gilbert Moreno Thomas M. Jahns (UW–Madison) Seth McElhinney (UW–Madison)

ape030_bennion_2012_o.pdf

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